1. Field of the Invention
The present invention relates to a steering apparatus for vehicle having a variable transmission ratio of a steering angle of turned wheels to a steering angle of a steering wheel.
2. Related Background Art
In the comparative steering apparatus, rotation of a steering shaft coupled to the steering wheel is normally converted to lateral displacement of a tie rod through a gearing system, such as a rack and pinion.
The apparatus employs a transmission ratio changing mechanism for changing a rotation transmission ratio between the input shaft and the output shaft (hereinafter referred to as a transmission ratio) by rotationally driving a gear forming a gearing system by an actuator on this occasion. For example, as shown in FIG. 6, transmission ratios are changed according to vehicle speeds V, thereby assuring driving stability according to the vehicle speeds V.
In order to provide against failure of the transmission ratio changing mechanism described above, the steering apparatus disclosed in Japanese Laid-open Patent Application No. 62-23869 is so arranged that a base transmission ratio (a base gear ratio) Gb as a transmission ratio between the input shaft and the output shaft in a state in which the actuator of the transmission ratio changing mechanism is at a stop is set at a middle point of the transmission ratio variable range VR. Under this setting, even in the event that the actuator for changing the transmission ratio comes to a stop, the apparatus can avoid the situation where the transmission ratio change becomes larger than during the normal operation, thereby relieving a feeling of incompatibility which a driver has.